test _determine_intersection (mpytools#208)

* test _determine_intersection

* changelog

Author: mathause

CHANGELOG.md

@@ -22,7 +22,8 @@
 
 - Add python 3.13 to list of supported versions ([#158](https://github.com/mpytools/mplotutils/pull/158)).
 - Increased test coverage ([#180](https://github.com/mpytools/mplotutils/pull/180), [#181](https://github.com/mpytools/mplotutils/pull/181),
-  [#182](https://github.com/mpytools/mplotutils/pull/182), and [#207](https://github.com/mpytools/mplotutils/pull/207)).
+  [#182](https://github.com/mpytools/mplotutils/pull/182), [#207](https://github.com/mpytools/mplotutils/pull/207),
+  and [#208](https://github.com/mpytools/mplotutils/pull/208),).
 
 ### Bug fixes
 

mplotutils/_cartopy_utils.py

@@ -479,7 +479,7 @@ def _determine_intersection(polygon, xy1, xy2):
         arr = np.atleast_2d(arr)
     elif isinstance(intersection, shapely.geometry.LineString):
         if intersection.is_empty:
-            return np.array([])
+            return np.array([[]])
         else:
             return np.array(intersection.coords)
     else:

mplotutils/tests/test_mapticklabels.py

@@ -1,6 +1,7 @@
 import cartopy.crs as ccrs
 import numpy as np
 import pytest
+import shapely
 
 import mplotutils as mpu
 
@@ -109,3 +110,46 @@ def test_xyticklabels_not_on_map():
 
 #         assert ax.texts[0].get_text() == "60°E"
 #         assert ax.texts[-1].get_text() == "60°W"
+
+
+def test_determine_intersection():
+
+    box = shapely.box(0, 0, 1, 1)
+
+    # case 0 -> the expected two points top & bottom
+
+    a = shapely.Point((0.5, -0.5))
+    b = shapely.Point((0.5, 1.5))
+
+    result = mpu._cartopy_utils._determine_intersection(box, a, b)
+    expected = np.array([[0.5, 0.0], [0.5, 1.0]])
+
+    np.testing.assert_allclose(result, expected)
+
+    # case 1 -> only one intersection (not sure how this would happen)
+
+    b = shapely.Point((0.5, 0.5))
+
+    result = mpu._cartopy_utils._determine_intersection(box, a, b)
+    expected = np.array([[0.5, 0.0]])
+    np.testing.assert_allclose(result, expected)
+
+    # case 2 -> intersection along a polygon edge
+
+    b = shapely.Point((1, 1.5))
+    a = shapely.Point((1, -0.5))
+
+    result = mpu._cartopy_utils._determine_intersection(box, a, b)
+    expected = np.array([[1.0, 0.0], [1.0, 1.0]])
+
+    np.testing.assert_allclose(result, expected)
+
+    # case 3 -> no intersection
+
+    a = shapely.Point((1.5, -0.5))
+    b = shapely.Point((1.5, 1.5))
+    result = mpu._cartopy_utils._determine_intersection(box, a, b)
+
+    expected = np.array([[]])
+
+    np.testing.assert_allclose(result, expected)